1. Field of the Invention
The present invention relates to processes for producing oxidative cross-linked polyarylene sulfide. More specifically, the present invention relates to a process for producing oxidative cross-linked polyarylene sulfide having an improved productivity, which enables reduction in the amount of gas generated during a melting step in an oxidative cross-linked reaction that is carried out after polymerizing polyarylene sulfide.
2. Description of Related Art
Polyarylene sulfides, a typical example of which is polyphenylene sulfide, have excellent heat resistance and chemical resistance properties and are widely used for producing molded products of electrical components, electronic parts, and automotive products as well as fibers and films.
As an example of methods for preparing polyarylene sulfide, a sulfide agent, such as sodium sulfide, and sodium hydrogensulfide, is reacted with a polyhaloaromatic compound, such as p-dichlorobenzene, in an organic polar solvent, such as N-methyl-2-pyrrolidone (hereinafter also referred to as NMP). In an injection molding application, in general, crude polyarylene sulfide obtained in the above reaction is washed with water to remove salt byproducts and is then subjected to an oxidative cross-linking reaction so as to become highly viscous. In this manner, a final product having desired mechanical characteristics and mold processibilities can be obtained.
The above-mentioned oxidative cross-linking reaction of polyarylene sulfide is conventionally carried out using a batch process. For example, Japanese Unexamined Patent Application, First Publication No. Sho 62-205127 discloses a technique in which the aggregation of polyphenylene sulfide particles during an oxidative cross-linking reaction can be prevented by carrying out an oxidative cross-linking reaction of uncross-linked polyarylene sulfide in a vessel-rotation type heating device having no agitation blades.
However, although the vessel-rotation type heating device used in the method described in the above publication has an advantage, as compared with a conventional device provided with agitation blades which is used in a batch type oxidative cross-linked method, in that unnecessary shearing force is not applied to the particles of polyarylene sulfide to avoid the aggregation of the particles, and it is of great practical use, a supplying and discharging amount of oxygen containing gas used in the method cannot be increased due to problems associated with the structure of the heating device, and hence, the productivity of oxidative cross-linked polyarylene sulfide is significantly decreased. In addition to that, removal of gas components becomes insufficient, and some gas components remain in polyarylene sulfide obtained. Here, the term xe2x80x9cgas componentsxe2x80x9d means volatile substances contained in polyarylene sulfide, or components whose molecular weight is decreased due to thermal decomposition, etc. If the removal of the gas components is insufficient, corrosion of a metal mold by the gas components during a molding process, or clogging in a gas vent, i.e., a phenomenon in which tar-like substances adhere to a vent pipe during a molding process and clogs the pipe, may occur.
Accordingly, an object of the invention is to provide a method for preparing an oxidative cross-linked polyarylene sulfide resin with excellent productivity in which gas components present in polyarylene sulfide are effectively removed during an oxidative cross-linking reaction of polyarylene sulfide to be a desired melt viscosity after polymerizing polyarylene sulfide.
The inventors of the present invention, after diligent studies on solving the above object, found that not only can the oxidative cross-linking reaction of polyarylene sulfide be enhanced and the productivity thereof increased, but also that gas components present in polyarylene sulfide can be effectively removed, if a reaction apparatus including a reaction vessel and a transverse type heating member having a helical structure, which is rotatable around a central shaft disposed in the reaction vessel, is used, and heated oxygen containing gas is supplied to the polyarylene sulfide from the downward direction of the transverse type heating member via a gas inlet while the polyarylene sulfide is heated and agitated by the rotation of the transverse type heating member. Based on these findings, the inventors of the present invention completed the present invention.
Accordingly, the present invention provides a process for producing oxidative cross-linked polyarylene sulfide using a reaction apparatus including a reaction vessel provided with a resin inlet, a gas inlet, a resin outlet, and a gas outlet, and a transverse type heating member having a helical structure which is rotatable around its axis disposed in the reaction vessel, comprising the step of: supplying heated oxygen containing gas to the polyarylene sulfide from the downward direction of the transverse type heating member while the polyarylene sulfide is heated and agitated by the rotation of the transverse type heating member to carry out an oxidative cross-linking reaction of the polyarylene sulfide.
According to the above process for producing oxidative cross-linked polyarylene sulfide of the present invention, it becomes possible to increase productivity, and the gas components present in polyarylene sulfide can be effectively removed.
Hence, the oxidative cross-linked polyarylene sulfide produced by the method according to the present invention can be widely used as various molding materials or as materials for fibers, electric and electronic parts, parts for automobiles, and coating.